In our PCT patent application PCT/EP89/01437 (Publication No. WO 90/06418) we describe an apparatus for connecting and disconnecting threaded members, which apparatus comprises a power tong having a pipe receiving recess and a jaw assembly for gripping and rotating a first pipe, a back-up unit having a pipe receiving recess and means for gripping a second pipe, and means for transmitting reaction forces generated by said power tong to said back-up unit, which means comprises:
a first member connected to one of said power tong and said back-up unit remote from the pipe receiving recess thereof and to the other of said power tong and said back-up unit to one side of the pipe receiving recess thereof; and
a second member connected to said one of said power tong and said back-up unit remote from the pipe receiving recess thereof and to said other of said power tong and said back-up unit to the other side of the pipe receiving means thereof,
wherein said apparatus comprises dynamic means for transmitting compressive and/or tensile forces in one of said first and second members to the other of said first and second members.
In the embodiments described in FIGS. 2 and 3 of said PCT patent application, said first member and said second member each comprise straps and said means for transmitting compressive and/or tensile forces in one of said first and second members comprises a third member (a tube) mounted for pivotal movement on one of said power tong and said back-up unit about an axis extending between said first member and said second member, said third member having a first tension arm and a second tension arm extending away from said axis, said first member being pivotally connected to said first tension arm and said second member being pivotally connected to said second tension arm.
Whilst the arrangement shown works admirably for most purposes it has the limitation that the power tong and the back-up unit cannot be moved close together.